A mix drink shot. Often in a double shot glass.
For those who cannot or aren't interested in taking a regular shot. Usually 2 thirds liquor 1 third mixer of choice, but also can be a regular shot with just a splash of a mixer.

"Hey man, pour this girl a dirty nipple!"
"I don't know if i can take a shot right now, give me a dirty nipple."
A Common Dirty Nipple
1 (double) shot glass
2/3rds Ciroc Vodka